Production of sodium 1, 5-borate



Nov. 28, 1961 D. s. TAYLOR ET AL PRODUCTION 0F soDIUM 1,5-BORATE 2Sheets-Sheet 1 Original Filed May 25, 1955 ./lffLso/VPMES, .INVENToRNov. 28, 1961 D. s. TAYLOR ETAL 3,010,786

PRODUCTION OF' SODIUM 1,5-BORATE Original Filed May 23, 1955 2Sheets-Sheet 2 5cl-fc C'a/c/hed ci Hamac .00A/ALU 5. 72H/L0@ IN VENTORS.

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United States Patent O 3,010,786 PRDDUCTIN OF SDIUM 1,5-BORATE v DonaldS. Taylor, Whittier, and Nelson I. Nies, Laguna Beach, Calif.,assignors, by inesne assignments, to United States Borax & ChemicalCorporation, a corporation of Nevada Original application May 23, 1955,Sei'. No. 510,130, now Patent Iso. 2,886,461, dated May 12, 1959.Divided and this application Dec. 5, 1955, Ser. No. 778,449 2 Claims.(Cl. 23-59) This invention has to do with the production of thecrystalline sodium boi-ate Na2O-5B2O3l0H2G, which is commonly known assodium pentaborate and which will be referred to herein as sodium1,5-borate in accordance with the nomenclature recommended by theinternational Union of Chemistry.

The invention provides particularly convenient and economical proceduresfor producing sodium 1,5-borate for any desired purpose. The presentinvention is also capable of producing directly sodium 1,5-boratecompositions that are especially satisfactory as furnace feed for theproduction or' certain anhydrous sodium borate compositions. Theproduction of such anhydrous sodium borate compositions, which aresubstantially crystalline and have a percentage content of B203typically exceeding 80%, is more fully described and claimed in ourcopenoing patent application, Serial Number 510,130, led lvlay 23, 1955,now Patent lso. 2,886,461, and entitled Anhydrous Crystalline Borate andlrocess for Producing Same, of which the present application is adivision. That parent application is a continuation-impart of ourcopending patent application, Serial Number 348,672, filed on April 14,i933, now abandoned.

ln accordance with one aspect of the present invention, sodium1,5-borate is typically produced by supplying boric acid and sodium1,2-borate contmuously to a rotary calciner to which a controlled streamof air is also supplied in a manner to be described.

in accordance with a further aspect of the invention, sodium 1,2-oorateand boric acid are supplied substantially continuously to an aqueousslurry, and sodium 1,5-borate is crystallized from the solution phase ofthe slurry continuously at substantially constant temperature.

A full understanding of the invention and of its further objects andadvantages will be had from the following description of certainillustrative manners of carrying -it out. That description, of which theaccompanying drawings form a part, is intended only as illustration, andnot as a limitation upon the scope of the invention, which is defined inthe appended claims.

ln the drawings:

FlG. 1 is a schematic vertical section representing an illustrativefurnace such as may be used for producing anhydrous sodium borate; l

FiG. 2 is a schematic drawing representing an illustrative system inaccordance with the invention;

FlG. 3 is a graph, representing the relative hygrocopicity of certaincompositions plotted against percentage B203;

FlG. 4 is a schematic drawing representing a modied illustrative systemin accordance with the invention; and

FIG. 5 is a schematic drawing representing a further modification.

Furnace operation As described in the above identified parentapplication, crystalline anhydrous sodium berate of the type describedmay be produced from a furnace melt that comprises as raw material amixture of boric acid and a form of sodium 1,2-borate having less thanthe normal Water content of l0 mols H2O per mol of sodium 1,2-borate.

lflifi Patented Nov. 28, 1961 Such a melt may be formed, for example, ina furnace of the type indicated partly schematically in FIG. l. Afurnace enclosure Ztl comprises side Walls 22, oor 27 and ceiling 21.The feed material may be introduced by any suitable conveyor anddistributing means7 not shown, at the top of the furnace side walls 22,as indicated by the arrows 23, and forms a bank 24 of solid materialsurrounding the furnace outlet, indicated at 26 in the door 27 of thefurnace enclosure. The slanting face of bank 24 is exposed directly toheat from an open flame within the furnace enclosure. That flame istypically produced by combustion of natural or artificial gas at aburner, indicated schematically at 2S. Feed material is thereforecontinuously melted at the exposed face of bank 24, and ows down thesloping surface of the bank to furnace outlet 26. That outlet may bedesigned and operated in known manner to regulate within limits thetemperature at which the melt is delivered from the furnace. Thatdelivery is typically directed, as by the spout 30, to a series ofrelatively deep tray-like molds 32, which may be moved under the spouton any suitable conveying means, indicated at 34. in a furnace of thattype the feed material typically remains solid at the upper portion ofthe sloping banks 24, being gradually heated as it moves down the banks,and starting to melt only after'it has moved down the slope aconsiderable distance. It is therefore desirable that the feed comprisea composition that remains free-flowing during that initial heatingstage.

1f the feed material initially contains an excessive amount of water itis found that it may, under extreme conditions, become so uid uponheating as to run down the furnace banks without becoming dehydrated.With more moderate excess of Water, the feed material tends to formlumps and balls as the water is released with increasing temperature,impeding the free ow of the material down the furnace banks. 'Ihatdifficulty may be greatly reduced by utilizing a furnace feed havingreduced water content.

Furnace feed: Borz'c acid and calcined borax Such a furnace feed maycomprise, for example, a mixture of boric acid and calcined borax. FIG.2 represents in schematic form an illustrative system for providing sucha furnace feed. Borax is delivered from a storage bin 39 to a suitabledehydrator, which is indicated at 40 as a conventional calciner. Inactual practice any suitable type of dehydrating means may be employed,and the numeral 4l) may, for example, represent a series of individualcalciners, or any other known means of removing a large proportion ofthe water of crystallization of the borax. Calcined borax is deliveredto surge bin 42 from dehydrator 40 preferably with a water contentbetween 1 and 2 mols of Water per mol of sodium tetraborate. Thecalcined borax is supplied via a suitable metering device, indicatedschematically at 43, to the dry mixer 46. Boric acid from a storage bin44 is similarly supplied via the metering device 45 to dry mixer 46. Thetwo metering devices are regulated in suitable mutual relation, asindicated by the dashed line 47, to supply calcined borax and boric acidto the dry mixer in a predetermined proportion. The proportion of thoseingredients is so determined, taking account of the average Watercontent of the calcined borax produced by dehydrator 40, as to yield amixture at the outlet of mixer 46 that has the desired average molarratio. For example, if the borax is calcined to a water content of l.mol, equal parts by weight of the calcined borax and boric acid provideof water. The mixture from mixer 46 is then supplied via any suitableconveying and metering means 48 to the furnace, indicated at 50.

By proportioning the boric acid and calcined borax to yield a molarratio equal toeabout 3.85, for example, on the basis of the averagewater content of the calcined borax, such small irregularities in thatwater content as normally occur in calcined borax need not be constantlymonitored by laboratory analysis and compensated by adjustment of theproportions of the ,two ingredients. Although such normal irregularitiesin water content may lead to corresponding variations in ratio of boricacid to anhydrous sodium 1,2-borate in the actual mixture pro` duced,thus causing slight variations in the molar ratio of the furnace feed,that ratio will ordinarily remain within the preferred range betweenabout 3.7 and 4.0, .and will therefore not disturb proper operation ofthe process. `In that manner it has been found to be possible to produceeconomically a very satisfactory product from an initial Vfurnace feedcomprising a simple mixture of boric acid and calcined borax.

Furnace feed: Boric acid and sodium 1,2-brae pentahydrate Alternatively,the calcined borax at bin 42 may be replaced by crystalline sodium1,2-borate pentahydrate. Such use of pentahydrate and boric acid has theadvantage that both components of the mixture are definite crystals ofuniform composition. For example, a mixture of one part sodium1,2-borate pentahydrate and 0.807 part boric acid by weight leadsconveniently kto a uniformly repro- 'd-ucible furnaceV feed having molarratio VB203/Na20 of approximately 3.90, which is within the preferredrange. Furnace feed of that illustrative type contains substantially36.5% water. That ligure, although it is Very appreciably less Vthan the45.8% water content of a corresponding mixture of boric `acid andordinary borax, is high lenough to require careful and continuouscontrol of the rate of supply of the feed material to the furnace atsuch a value that the material moves uniformly down fthe furnace banksand becomes fully dehydrated before reaching the furnace outlet. it isfound preferable under most conditions of operation to employ a furnacefeed composition containing less than about 30% water, such, forexample, as a mixture of boric acid and calcined borax `containing lessthan 2 mols of water per mol of sodium V1,2-borate.

H ygroscopz'czty of product content by weight of B203 is plotted asabscissa. The

ordinates are plotted on a logarithmic scale and represent the`percentage increase in weight of samples of the indicated materialswhen exposed tovan atmosphere of approximately 52% relative humidity atroom temperature for a period of ten days. All materials were ingranular form and of a screen size to pass a 35 mesh Tyler screen v'andto be held ona 48 mesh screen.

The fsharp increase of hygroscopicity with B203 content in thenon-crystalline sodium borate materials throughout the range between77.1% B203 (anhydrous 'sodium 1,3-borate) and about 86.5% B202 isclearly shown -by curve A of FIG, 3. The Vamounts of water picked up Vbycrystalline anhydrous sodium l,2-borate and by crystalline anhydrous`boric oxide v(at left and right t' extremes of curve B) are more thandouble the amounts for the correspondingV glassy materials. relation issharply and surprisingly inverted for anhydrous e Molar ratio ofB203/Na2`0 The invention not only utilizes the newly discovered lowhygroscopicity of anhydrous crystalline sodium 1,4- borate, theunexpected nature of which is clearly illustrated in FIG. 3, but furthermakes use in a novel manner of the sharp dependence upon B203 content ofthe hygroscopicity of glassy anhydrous sodium 'borates By working in therange of B202 content that corresponds to Va molar ratio between 'about3.7 Vand 4.0, the invention makes practical use of `that relationship inthe following way. As a melt having molar ratio in that range coolsunder the conditions already described, Na20-4B2O3 crystallizes and isremoved from the liquid phase yof the melt. The molar ratio of theremaining melt is therefore shifted progressively further away from thevalue (4.0) 'of the crystal formed. Any relatively `small portion ofthat remaining melt that may ultimately form glassy rather themVcrystalline portions of the final integrated solid thereforenecessarily has a molar ratio appreciably less than 4.0. Because of thesharp slope of curve A in FG. 3, such glassy portions can at -mostVcontribute only a relatively small amount to the hygroscopicity of theoverall integrated composition. For instance, with an initial furnacemelt having the preferred molar ratio 3.85, and assuming, as a ratherextreme example, that on cooling of such a melt only 85% of its B203-crystallizes as Na20-4B203, the Vrernainderof the composition wouldhave average molar ratio of 3.19 vand a corresponding percentage B203content of'78.2%. That substantially corresponds to the composition ofanhydrousV sodium 1,3-borate, tending Yto facilitate crystallization ofthat substance. However, even if all of that remainder should Vformglass, it may be seen from FIG. 3 that the tendency of that fraction ofthe final physically integrated composition to absorb moisture `would beonly about onehalf as great as would be the case if 15% of a compositionof molar ratio 4.0 should fail to crystallize.

Moreover, a composition having a nominal molar Yratio of 4.0 is likely,as has already been indicated, -to include portions for which the Aratiohas a value appreciably above 4.0. Any such portions of furnace -meltproduce upon cooling a .mixture of crystalline 1,4-borate land a glassymaterial for which the molar ratio is markedly displaced upward from'4.0. Such glassy material, as may be seen from FIG. 3, has aVrelatively great tendency to absorb water from the atmosphere.-Glassymaterialof that type is effectively avoided in accordancerwiththe parent irivention, and the water absorption of any glass that mayform is, held to a minimum value, by maintaining the average'molar ratioof the furnace'feed less than 4.0 and preferably within the rangebetween 4.0 an'd'about 3.7.

Elimination of boric acid lt has been discovered further, that, whereassatisfactory results are obtainable with feedcompositions of the typealready described, it is preferable from the point of view of economicaland uniform feeding and opera- `tion of the furnace, that the furnacefeed bersubstantially Y that superior behavior is obtainable byutilizing as feed However, that 'Y a composition consisting essentiallyof sodium 1,5-borate, either crystalline or partially'orwhollydehydrated, andV a sufllcient quantity tof a sodium borate having aBgOs/NaZO ratio less than 4 to provide the desired overml ratio of thecomposition. A preferred sodium borate for that latter purpose is sodiuml,2borate. For eX- ample, a suitable feed composition in accordance withthe present aspect lof the invention comprises sodium 1,5- borate andsodium l,2-borate in a ratio of 2 mols 1,5- borate to approximately lmol l,2-borate. For a given total water content, a composition of thattype, for example, gives appreciably better performance in the furnacethan a corresponding mixture of boric acid and sodium l,2borate.

Reaction of borax and boric acid in calciner One aspect of the presentinvention has to do with procedures for producing a furnace feedmaterial of the type just described in a particularly economical andconvenient manner. FIG. 4 illustrates schematically a typical system forcarrying out one illustrative procedure of that type. Borax and boricacid are delivered from respective bins 60 and 6l in a denite proportioncontrolled, for example, by the metering devices 62 and 63,respectively. ln preferred form of the invention, the ratio of thoseingredients is so determined as to provide substantially 6 mols of boricacid per mol of sodium 1,2-borate, giving an overall molar ratioB2O3/Na20 of approximately 5, corresponding to the composition of sodiuml,5borate. Alternatively, a larger proportion of borax may be used, aswill be described below. rThose ingredients are thoroughly m'nred, as at65, and are supplied at a controlled and relatively low rate of flow, asvia the metering device '66, to a calciner, indicated schematically at79. That calciner is supplied, by means indicated at 72, with a streamof air of accurately controllable volume and temperature. That air movesthrough the calciner in countercurrent flow with respect to thedescribed feed mixture, entering at the discharge end 73 of the calcinerat moderate temperature, and leaving at the feed end 74 of the calcinerat relatively low temperature.

Calciner 70 is operated at relatively low temperature throughout, andparticularly in the vicinity of the feed end. As an illustration, airmay enter at 73 at a temperature of 200 to 300 F., and preferably leavesthe calciner at 74 at a temperature within the range between about 85and about l00 F. A relatively large volume of air is employed,approximating 200 cu. ft. per pound of material processed, that largevolume making up for the relatively low moisture-carrying capacity ofthe air at the temperatures indicated.

Under the conditions described in the vicinity of the feed end or" thecalciner, it has been found that chemical reaction of the borax andboric acid to form sodium 1,5-borate can be readily im'tiated, andordinarily is so initiated spontaneously. 'That reaction, as is wellknown, releases water in a theoretrical amount of 9 mols H2O per mol ofl,5borate formed. vlf allowed to continue in a closed vessel, forexample, that released water typicaliy leads to a slurry, or even asolution, depending upon the temperature. An important feature of thepresent invention is that the conditions are so controlled that thereaction proceeds at a moderate rate, and that a large fraction of thereleased water is evaporated as it is released. That is accomplishedprimarily by providing a elatively rapid flow of air at a moderately lowtemperaare. The volume of air is limited sufliciently that a controlledamount of released water is permitted to accumulate, sufficient to makethe entire granular mixture snpercially damp. That supercial dampness isan important feature of the process, since it promotes the describedchemical reaction. The rate of evaporation, on the one hand, must besufficient to avoid too great Wetness of the material which would tendto produce excessive agglomeration or balling of the material, reducingits effective surface area and further slowing evaporation.

5 On the other hand, the rate of evaporation must not be too great, forthe mixture then may become so dry as to slow down the chemicalformation of 1,5-borate. That would reduce the rate of release of water,and so tend further to increase the dryness.

The operation is thus carried out under conditions that are notinherently stable, but that tend, 'once they have been altered in eitherdirection, to change further in that same direction. It has been found,however, that by careful control, particularly of the volume 0f air flowthrough the calciner, it is possible to maintain satisfactoriiy uniformconditions of fop-eration. Those conditions, as already indicated, aresuch that the transformation of borax and boric acid to sodium1,5-borate takes place gradually as the material moves through a dampzone of appreciable length, the released water being evaporated at sucha rate as to maintain throughout that zone a condition of moderatesuperficial danipness. Moreover, as the material progresses through thatdamp zone the temperature of the air that it encounters, and also thetemperature of the material itself, gradually increases. For example,the transformation to 1,5-borate typically starts in the immediatevicinity of the feed end of the calciner at a temperature of less thanF. and is not fully completed until the material has passed aconsiderable distance along the calciner, where it is exposed to air ata temperature of to 150 F., for example. That higher temperature tendsto insure complete reaction.

After the reaction has reached substantial completion, the surfaces ofthe sodium 1,5-oorate particles become dry. The 1,5-borate may then bedelivered from the calciner in surface-dry condition and stillcontaining substantially the normal 10 mols of water per mol of i,5borate. Alternatively and preferably the calciner is of such length thatthe surface-dry 1,5-borate is retained in the calciner for a suicienttime to become calcined, losing a large fraction or even substantiallyall of its water of crystallization. In the preferred form of theinvention, the moist Zone in which the chemical reaction primarilyoccurs occupies roughly one-half of the length of the calciner, whilethe remainder 'of that length provides a Zone of considerably highertemperature in which 'the dry 1,5-borate is calcined. At the dischargeend of the calciner the l,5borate is typically exposed to air at atemperature of 200 to 300 F., for example, which is Sufficient to reducethe remaining water content of the 1,5-borate to as little as 2 to 4mols. Alternatively, temperatures higher than 300 F. may be employed forthe last portion of the described operation. That is particularlyconvenient if the damp phase and the calcining phase of the operationare provided with separate air streams that are subject to independentcontrol, as may be accomplished, for example, by the use of separatecalciners for the two phases of the process. By the use of airteinperatures in the neighborhood of 600 F. the finally deliveredmaterial may then oe dried substantially completely, typicallycontaining as little as 1% water, or about 0.25 mol H2O per moll,5borate.

The product of that described operation is substantially sodium1,5-borate, preferably considerably dehydrated. That product may bedelivered via a surge bin 83 and metering device 84 to a dry mixer 80,to which is also supplied at an appropriate rate a sodium berate havingmolar ratio less than 4. As typically illustrated in FIG. 4, ordinarycalcined borax is supplied from a storage bin 78 via a metering device79, the proportion of borax to 1,5-borate being determined in accordancewith their particular compositions to yield a composition in mixer 80having an average molar ratio preferably somewhat less than 4.0 for thereasons already discussed. That mixture, typically comprising from about1.3 to about 1.9 mols of sodium 1,5-borate per mol of sodium 1,2-borate,may then be supplied as feed material to the furnace, indicatedschematically at 82.

Direct production of furnace feed in calciner An alternative manner ofoperating `a system of the above Vdescribed. type includes supplying theborax and boric acid to mixer 65 in a proportion to yield a compositionhaving substantially the molar ratio desired for the furnace feeditself, preferably between about 3.7 and 4.0. That range of molar ratioscorresponds to a mixture of borax and boric acid containing between 1.5and about 1.8 molsof sodium 1,2-borate'per 6 mols of boric acid, orbetween 0.5 and 0.78 mol excess over the 1.0 mol of 1,2-borate requiredto react with 6 mols of boric acid.

VThe operation then proceeds substantially as already described, exceptthat in calciner 70 there is an excess of yborax beyond that required toreact with all the boric acid. Bin 78, metering device 79 and dry mixer80 may then be omitted, the calcined product from surge bin 83 `beingsupplied directly via metering means 84 to the furnace. Under thatmanner of operation all of the boric acid is typically converted tosodium 1,5-borate in the damp phase of the operation, while from 33 -toabout 44% of therinitial -borax remains unreacted. -During the calciningphase, both the remaining borax and the 1,5- borate produced by 4thereaction are dried to respective degrees dependent upon the particularconditions employed. A particular advantage o-f that manner of operationis that the mixture of borax and sodium 1,5-borate behaves-particularlywell during calcining, and can be made virtually completely anhydrouswithout diiiicul-ty.

VA further advantage of mixing borax and boric acid initially in theproportion required to give the final furnace feed is that thecomposition of both borax and boric acid is substantially uniform, andit is unnecessaryrto vary the weight ratio in which they are combined tocompensate for variations in composition of the ingredients.

In a process of the type described in which sodium 1,5- borate isproduced under conditions of only superficial dampness, it is Ifoundadvantageous, although not necessarily essential, to pro-vide more orless continuous seeding with crystals of 1,5-borate. That may ordinarilybe accomplished to a sufficient extent when the operation is carriedout, as illustratively described, in a calciner with counter-current airow, since iine crystals of 1,5-borate formed by the process tend -to becarried by the air stream toward the feed end of the calciner, wheretheyY act as seed crystals. Alternatively, a definite amount of theproduct may be removed from the calcining zone of the `operation andrecycled through the damp reaction zone. Such recycling of a portion ofthe product is indicated schematically at 71 in FIG. 4. That not onlypromotes the reaction, but facilitates removal of the released water.

Reaction of borax and boric aci-dias a slurry so that the addedmaterials lare held in suspension. Tank 90 is maintained at a suitablemoderately-elevated temperature, for example 100 F., at which borax andboric acid are decidedly more soluble ythan sodium 1,5-borate insolution saturated with respect to the latter. The added borax and boricacid then go into solution rapidly, the granules of those materialsdisappearing substantially as soon as they are introduced into the tank.rIhatV produces a solution appreoiably supersaturated with respect tosodium 1,5-borate, causing the latter substance to crystallize outrapidly. Therefore, evenV when borax and Aboric acid are added steadilyto the Vtank, the result-V ing slurry contains 'substantiallyV no solidmaterial except sodium 1,5-borate. The 1,5-borate is typically recoveredcontinuously in any convenient manner, 'for example Vby centrifugingvsuspension withdrawn from the bottom of the tank, as indicatedvschematically at 94. The liquors from the centrifuge are typicallyreturned via a storage ltank to tank '90, as indicated at 96. The dampcrystals of sodium 1,5-borate recovered from the centrifuge aretypically supplied -directly to a calciner-9.7, in which any desiredfraction of their water of crystallization is removed.

It is preferred to provide the sodium 1,2-borate to tank 90 in the formof calcined 'borax containing approximately 1 mol of water per mol ofsodium 1,2-borate. A source of calcined borax of thattype is representedschematically as the ybin 92, :from which the material is supplied totank 90 via the metering device 93.V The boric acid supply to tank 90 istypically shown as including a bin 88 and metering 'device 89, the twometering means 89 and 93 being operated under suitable related control,in the manner previously described. An important advantage of supplyingthe borax in highly calcined form is that the amount of water ofhydration carried into tank 90 with the borate and boric acid issubstantially equal to the Water carried away from the tank as water ofcrystallization of the sodium 1,5-b0rate produced. The equationexpressing .that relation is herewritten as follows:

Accordingly, tank 90 is typically operated continuously in the mannerdescribed, producing sodium 1,5-borate crystals in a very convenient andeconomical manner, without requiring that any of the mother liquor `bediscarded or that water vbe evaporated in appreciable quanttty.

In the illustrative operation described, the material delivered bycalciner 97 is typically calcined sodium 1,5- borate. That material issatisfactory for use as the major component of a highly desirablefurnace feed, a suitable amount of another sodium borate being addedtoit to provide the desired overall molar ratio. As illustrativelyshown, the output of the calciner is taken to surge bin 98, and is thensupplied via metering device 100 to a dry mixer 102. fCalcined borax istaken from the same bin 92 that supplies tank 90, and is supplied via ametering device 101 to mixer 102. The ratio of calcined 1,5- borate andcalcined borax is controlled to give a mixture having the desired molarratio, and thatV mixture is then typically supplied to the furnace,indicated schematically at 82. Alternatively, for example, the molarratio of the product may be adjusted by adding another borate to thecrystalline 1.5-berate before it reaches calciner 97. When that is done,regular crystalline borax can be used instead of calcined borax foradjusting the molar ratio, the mixture of borax and 1,5-borate thenbeing calcined together. That procedure, again, has the advantagealready mentioned in another connection Vthat the two components of themixture are both crystalline in nature,

and subject to little or no variation in composition.

The systems illustratively shown in FIGS. 4 and 5 for producing suitablefeed materials for production of anhydrous crystalline borate, and whichutilize sodium 1,5- borate as one ingredient of such feed materials, areusable in part for the production of sodium 1,5-borate for conventionaluses as well.

We claim:

1. The process for producing sodium 1,5-borate crystals, which processcomprises the combination of adding substantially continuously to anaqueous solution in a vessel at a temperature of approximately 100 F.solid sodium 1,2-borate and boric acid in a molar ratio of substantially1 to 6, continuously agitating the resulting mixture substantiallywithout change of temperature to cause dissolution of the added solidsand simultaneous crystallization of sodium 1,5-borate, withdrawing fromthe ves- Ysel substantially continuously and simultaneously withseparating the crystals from said mixture, and returning the. resultingsolution to the vessel.

2. The process -for producing sodium 1,5-borate crystals, which processcomprises the combination of adding substantially continuously to anaqueous solution in a vessel at a temperature of approximately 100 F.solid sodium 1,2-borate containing substantially one mol of Water permol of sodium 1,2-borate and solid boric acid in a molar ratio ofsubstantially l to 6, continuously agitating the resulting mixturesubstantially without change of temperature to cause dissolution of theadded solids and simultaneous crystallization of sodium 1,5- borate,withdrawing from the vessel substantially continuously andsimultaneously with said addition a mixture of said solution andcrystalline sodium 1,5-borate, at substantially the said temperature,separating the crystals from said mixture, and returning the resultingsolu- 10 tion to the vessel, the Ywater carried into solution bydissolution of said solids substantially balancing the water carried outof solution by crystallization of the crystalline product.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Mellor: A Comprehensive Treatise on Inorganic and TheoreticalChemistry, vol. 5, page 76 (1924), Longmans, Green and Co.

1. THE PROCESS FOR PRODUCING SODIUM 1,5-BORATE CRYSTALS, WHICH PROCESSCOMPRISES THE COMBINATION OF ADDING SUBSTANTIALLY CONTINUOUSLY TO ANAQUEOUS SOLUTION IN A VESSEL AT A TEMPERATUE OF APPROXIMATELY 100*F.SOLID SODIUM 1,2-BORATE AND BORIC ACID IN A MOLAR RATIO OF SUBSTANTIALLY1 TO 6, CONTINUOUSLY AGITATING THE RESULTING MIXTURE SUBSTANTIALLYWITHOUT CHANGE OF TEMPERATURE TO CAUSE DISSOLUTION OF THE ADDED SOLIDSAND SIMULTANEOUS CRYSTAL-